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SubjectRe: usercopy whitelist woe in scsi_sense_cache
On Thu, Apr 12, 2018 at 8:02 PM, Kees Cook <keescook@chromium.org> wrote:
> On Thu, Apr 12, 2018 at 3:47 PM, Kees Cook <keescook@chromium.org> wrote:
>> After fixing up some build issues in the middle of the 4.16 cycle, I
>> get an unhelpful bisect result of commit 0a4b6e2f80aa ("Merge branch
>> 'for-4.16/block'"). Instead of letting the test run longer, I'm going
>> to switch to doing several shorter test boots per kernel and see if
>> that helps. One more bisect coming...
>
> Okay, so I can confirm the bisect points at the _merge_ itself, not a
> specific patch. I'm not sure how to proceed here. It looks like some
> kind of interaction between separate trees? Jens, do you have
> suggestions on how to track this down?

Turning off HARDENED_USERCOPY and turning on KASAN, I see the same report:

[ 38.274106] BUG: KASAN: slab-out-of-bounds in _copy_to_user+0x42/0x60
[ 38.274841] Read of size 22 at addr ffff8800122b8c4b by task smartctl/1064
[ 38.275630]
[ 38.275818] CPU: 2 PID: 1064 Comm: smartctl Not tainted 4.17.0-rc1-ARCH+ #266
[ 38.276631] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[ 38.277690] Call Trace:
[ 38.277988] dump_stack+0x71/0xab
[ 38.278397] ? _copy_to_user+0x42/0x60
[ 38.278833] print_address_description+0x6a/0x270
[ 38.279368] ? _copy_to_user+0x42/0x60
[ 38.279800] kasan_report+0x243/0x360
[ 38.280221] _copy_to_user+0x42/0x60
[ 38.280635] sg_io+0x459/0x660
...

Though we get slightly more details (some we already knew):

[ 38.301330] Allocated by task 329:
[ 38.301734] kmem_cache_alloc_node+0xca/0x220
[ 38.302239] scsi_mq_init_request+0x64/0x130 [scsi_mod]
[ 38.302821] blk_mq_alloc_rqs+0x2cf/0x370
[ 38.303265] blk_mq_sched_alloc_tags.isra.4+0x7d/0xb0
[ 38.303820] blk_mq_init_sched+0xf0/0x220
[ 38.304268] elevator_switch+0x17a/0x2c0
[ 38.304705] elv_iosched_store+0x173/0x220
[ 38.305171] queue_attr_store+0x72/0xb0
[ 38.305602] kernfs_fop_write+0x188/0x220
[ 38.306049] __vfs_write+0xb6/0x330
[ 38.306436] vfs_write+0xe9/0x240
[ 38.306804] ksys_write+0x98/0x110
[ 38.307181] do_syscall_64+0x6d/0x1d0
[ 38.307590] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 38.308142]
[ 38.308316] Freed by task 0:
[ 38.308652] (stack is not available)
[ 38.309060]
[ 38.309243] The buggy address belongs to the object at ffff8800122b8c00
[ 38.309243] which belongs to the cache scsi_sense_cache of size 96
[ 38.310625] The buggy address is located 75 bytes inside of
[ 38.310625] 96-byte region [ffff8800122b8c00, ffff8800122b8c60)


-Kees

--
Kees Cook
Pixel Security

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